The visual inspection of a generator field and a stator core should be performed on a periodic basis. Conventional generator field/stator core inspection and testing procedures typically require the complete disassembly of the stator core and the removal of the generator field before any inspections or tests can be performed on the unit. The costs of the disassembly and removal of the generator field, the time it takes to complete this process, and the dangers inherent in generator field removal have led to the occasional omission of the examination of the generator field and the stator core from routine outage schedules.
In-situ inspections of generators have been performed by employing poles, trolleys, and field turning techniques. These procedures generally have not accomplished the inspection task in a satisfactory manner.
Miniature air gap inspection crawlers (“magic”) are disclosed in commonly owned U.S. Pat. Nos. 5,650,579 and 6,100,711, the disclosures of which are hereby incorporated by reference. These crawlers are designed to pass through the radial air gap between the core iron and the retaining ring for an in-situ inspection of the generator field and stator core.
Video cameras and other inspection tools may be attached to the crawler to perform the inspection of the generator field and the stator core. For example, a high resolution video camera may provide a clear view of the stator core laminations, stator wedges, field wedges, and the inboard ends of the retaining rings. The crawler thus provides detection capability for loose stator wedges, vibration bar sparking, core lamination damage due to foreign objects, motoring and hot spots, field wedge arcing, and surface heating damage. Similarly, commonly owned U.S. patent application Ser. Nos. 11/163,196, 11/306,600, and 11/306,601 describe the ultrasonic inspection of the field and the stator core. These patent applications are incorporated herein by reference. Through the in-situ inspection the generator, information may be gathered on the overall condition of the generator that can help determine if removal of the field is necessary.
Although these known devices are adequate for in-situ generator inspections, they are largely limited to use with entrance gaps that are greater than about one half inch (about 12.7 millimeters). If the entrance gap is smaller than about one half inch (about 12.7 millimeters), the field generally must be pulled out of the stator for inspection.
Thus, there is a desire for an inspection device that can accommodate entrance gaps of less than about one half inch (about 12.7 millimeters). Preferably, the inspection device can provide visual inspection, ultrasonic inspection, wedge tightness testing, electric core testing, and other types of inspections and testing.